In the case where human beings sense colors visually, three kinds of fluorescent substances of R, G and B emit light of primaries upon irradiation with electron beam, and the illuminant colors are visually sensed as chromatic colors, as in color TV. In addition, when a dye or a pigment in the form of a particle aggregate or a layer aggregate is irradiated with sunlight or white light, visible light of specific wavelength is absorbed by the dye or the pigment, and as a result, a chromatic color that is an object color can be visually sensed. In the case where such illuminant colors or object colors are visually sensed, visible light of specific wavelength region is absorbed or transmitted or reflected according to structural properties and surface properties of a substance irradiated with light, and any one of a transmitted light color, an absorbed light color and a reflected light color is predominantly sensed with the eye as a chromatic color. Further, when substances are irradiated with sunlight or white light, various phenomena or color developments, such as light refraction of rainbow, light diffraction of liquid crystal, blue sky, light scattering of sunset glow, and interference colors of oil film on water surface, soap bubbles and opal, take place, and it can be said that all of them are properties of aggregated or dispersed fine particle substances.
Such structural properties and surface properties of the substances are described in various literatures. For example, in Japanese Patent Laid-Open Publication No. 206719/2001 (patent document 1), with regard to colors visually sensed, it is described that in case of a thin film (single-layer or multi-layer thin film of monodisperse titanium oxide) in which any color material such as a pigment is not used at all and monodisperse titanium oxide particles are piled on a substrate, the appearance color tone becomes an interference color tone of red to blue that is neither an object color of a dye or a pigment nor an illuminant color, according to the diameters of the particles. In Japanese Patent Laid-Open Publication No. 239661/2001 (patent document 2), it is described that a deposit of a regular periodic structure, which is obtained by aggregating and arranging monodisperse solid fine particles having a number-average particle diameter of 100 to 1000 nm and having light transmission properties on a surface of a liquid-repellent base layer of a synthetic resin or the like having a black or dark color so as to clearly see an interference color by means of drying, emits clear monochromatic light of an interference color. As the monodisperse colorless solid fine particles having light transmission properties, inorganic oxide fine particles, such as silica, alumina, titania, silica-alumina and titania-selenium, and organic polymer fine particles, such as (meth)acrylic resins, styrene resins and olefin resins, are described. Accordingly, any of the film and the deposit described in Japanese Patent Laid-Open Publication No. 206719/2001 and Japanese Patent Laid-Open Publication No. 239661/2001 undergoes development of visually sensed colors as structural properties and surface properties of the fine particles of colloidal particle size which are regularly dispersed or aggregated or laminated.
Further, there have been heretofore proposed various processes for producing particle laminates, comprising subjecting a solid-liquid dispersion or suspension containing monodisperse spherical fine particles dispersed as a dispersoid to casting, spraying, coating, migration or the like to arrange, align, dry and fix the particles and thereby regularly align the dispersoid spherical fine particles longitudinally and laterally on a flat base member. The particle laminate obtained by regularly aligning the spherical fine particles in the above manner is expected to exhibit various surface properties based on various properties inherent in the constituent particle substance. In particular, as the constituent particles become finer particles such as those having sizes of submicron order or nano order, the surface properties exhibited by the fine surface become more definite, and such constituent particles can be expected as functional substances having novel surface functions.
In addition to the object colors due to dyes or pigments or the illuminant colors such as those of color TV, there are interference colors as colors visually sensed, and as described above, in Japanese Patent Laid-Open Publication No. 206719/2001, there has been proposed a monodisperse titanium oxide single-layer or multi-layer thin film in which monodisperse titanium oxide particles using no colorant such as a pigment are piled on a substrate and an appearance color tone of which becomes an interference color tone of red to blue according to the diameters of the particles. It is also described that there can be formed a monodisperse titanium oxide thin film whose appearance interference color tone can be freely controlled from red to blue according to the particle diameters by changing the diameters of the monodisperse titanium oxide particles. In Japanese Patent Laid-Open Publication No. 239661/2001, it is described that a deposit of a regularly periodic structure, which is obtained by aggregating and arranging monodisperse solid fine particles having light transmission properties on a surface of a liquid-repellent synthetic resin base layer of a black or dark color having a lightness of not more than 6 and a saturation of not more than 8 in a standard color solid so as to clearly see an interference color, emits clear monochromatic light of an interference color. The uncolored solid fine particles constituting the deposit are monodisperse particles, and as the solid fine particles, inorganic oxide fine particles, such as silica, alumina, titania, silica-alumina and titania-selenium, and organic polymer fine particles, such as (meth)acrylic resins, styrene resins and olefin resins, are described. It is also described that the number-average particle diameter of the solid fine particles is in the range of 100 nm to 1 μm. In Japanese Patent Laid-Open Publication No. 213334/2004 (patent document 3), there is described a process for producing an orderly arranged multi-layer laminate structure, comprising subjecting a solid-liquid suspension containing spherical monodisperse polymer particles of 200 to 700 nm prepared by emulsion polymerization to dialysis to substantially remove an electrolyte from the suspension, drying (temperature: 60° C.) the suspension containing the spherical monodisperse polymer particles having an electric double layer formed thereon while allowing the suspension to stand still, and then chemically fixing the arranged particles which are in contact with one another.
Under such circumstances as mentioned above, regarding the color development as the structural properties and the surface properties of substances, the present inventors have already proposed a process for forming a dry particle laminate, comprising preparing an aqueous dispersion in which organic or inorganic monodisperse spherical particles of colloidal particle size (particle diameter: several hundreds nm) previously colored a black color type achromatic color of gray to black with a dye or a pigment are dispersed, forming a green sheet (or suspension layer) of a given thickness using the aqueous dispersion (or suspension), and then sufficiently drying the green sheet to densely align the organic or inorganic monodiserpse spherical particles of a black color type achromatic color longitudinally and laterally. When a surface of the dry particle laminate is irradiated with natural light (or white light) in the visible wavelength region of 380 to 780 nm, the vertically reflected light color visually sensed is a clear deep chromatic color of red, green or blue by virtue of the specific particle diameters of the spherical particles. That is to say, the dry particle laminate becomes an optical color-developing material.
Consequently, the optical color-developing material of a dry type which develops a chromatic color satisfies the following requirements (1) to (3). The colors developed by such material are apparently distinguished from the object colors of the conventional dyes or pigments or the illuminant colors of color TV or the like, and under irradiation with visible rays, clear chromatic colors are visually sensed. The present inventors call such an optical color-developing material a “structural color-developing material”.
(1) The dry laminate which develops a chromatic color visually sensed is a three-dimensional particle laminate having a surface wherein organic or inorganic monodisperse spherical particles of at least a black color type achromatic color such as gray, blackish brown or black are aligned longitudinally and laterally as previously described.
(2) The organic or inorganic monodisperse spherical particles of a black color type achromatic color are spherical fine particles having a specific particle diameter of colloidal particle size, namely, a mean volume diameter (d) of 130 to 350 nm.
(3) Attributably to the monodisperse spherical particles of specific particle diameter constituting the dry particle laminate, the surface of the particle laminate undergoes, as the structural properties, development of a chromatic spectral diffraction color, such as purple color, blue color, green color, yellow color and red color, according to the specific particle diameter under irradiation with visible light.
By the way, a dry process wherein a solid-liquid suspension containing dispersed fine particles of colloidal particle size is dried to form an aggregate or a laminate of the fine particles has been heretofore studied. When such a solid-liquid dispersion (suspension layer) having a considerable thickness is dried, the dispersoid colloidal particles are aggregated and aligned with the progress of drying, and usually, cracks due to shrinkage on drying tend to occur on the surface. It is general that the tendency of occurrence of such cracks due to shrinkage on drying is increased as the surface area of the suspension layer to be dried becomes larger or the thickness of the suspension layer becomes larger.
That is to say, in the drying of the solid-liquid suspension, numerous cracks ranging from cracks having a width of about 1 μm which are hardly observed with the naked eye to cracks having a width of several mm which can be readily observed with the naked eye are usually formed on the surface with the progress of drying. On the surface of the aqueous or oily dispersion containing fine particles, the suspended fine particles are aggregated and aligned by the capillary force with evaporation of water or an organic solvent, and the dispersion medium (may be a dispersion medium containing a binder resin component) present among the fine particles is so shrunk by drying that a uniform surface cannot be held, and this shrinkage remains as a crack.
In case of the conventional structural color-developing materials, even if no crack is observed on the surface, there is a tendency that the ordered structure includes a layer wherein the particles are not sufficiently aligned longitudinally and laterally or that an ordered structure wherein the particles are aligned in different directions is formed. In the existing circumstance, therefore, purity of the ordered structure has not been satisfied yet.
When the solid-liquid suspension is dried, the dispersed particles are aggregated to form an aggregate, but in usual, on the surface of such a solid-liquid suspension (or dispersion) layer, cracks tend to be formed because of shrinkage on drying. It is general that the tendency of occurrence of cracks due to shrinkage on drying is increased as the surface area of the suspension layer to be dried becomes larger or the thickness of the suspension layer becomes larger.
That is to say, in the drying of the solid-liquid suspension, numerous cracks ranging from cracks having a width of about 1 μm which are hardly observed with the naked eye to cracks having a width of several mm which can be readily observed with the naked eye are usually formed on the surface with the progress of drying. On the surface of the aqueous or oily dispersion containing suspended fine particles, the suspended fine particles are aggregated and aligned by the capillary force with evaporation of water or an organic solvent, and the dispersion medium (may be a dispersion medium containing a binder resin component) present among the fine particles is so shrunk by drying that a uniform surface cannot be held, and this shrinkage remains as a crack.
Then, in Japanese Patent Laid-Open Publication No. 59210/2003 (patent document 4) that is a previous application for patent, the present inventors have proposed a method for aggregating and aligning spherical fine particles in a non-dry system to form a three-dimensionally ordered lattice from the spherical fine particles of colloidal particle size in the solid-liquid suspension. This method comprises immersing a pair of electrode plates in the suspension containing colloidal particles and performing electrophoresis to deposit (or electrodeposit) a particle laminate on the electrode plates, and this method is a method enabling particle alignment free from cracks due to shrinkage on drying.
The thus deposited particle laminate that is a three-dimensionally ordered lattice formed by electrophoresis is an optical color-developing material undergoing clear chromatic color development and is a three-dimensionally ordered lattice formed in a non-dry system.
In Japanese Patent Laid-Open Publication No. 73123/2003 (patent document 5) that is a previous application for patent, the present inventors have proposed a particle laminate as an optical color-developing material. This particle laminate is obtained by casting a solid-liquid suspension containing colloidal particles onto a sheet (flat base member, referred to as a “color-developing substrate sheet”) provided with regularly arranged deep-ditch divisions having an opening of 50 to 170 μm and an aspect ratio of 0.4 to 0.8, similarly to a mesh material, to form a suspension layer of a given thickness and drying the layer at a temperature of 50 to 60° C., and this particle laminate is effectively prevented from occurrence of cracks due to shrinkage on drying and develops a clear chromatic color.
That is to say, the optical color-developing material (particle laminate) proposed by the present inventors in the above specification is as follows.
(1) The particle laminate which develops a chromatic color visually sensed is a particle laminate having a surface wherein organic or inorganic monodisperse spherical particles of a black color type achromatic color are regularly aligned longitudinally and laterally.
(2) The organic or inorganic spherical particles constituting the laminate surface are monodisperse spherical particles of at least a black color type achromatic color such as gray, blackish brown or black.
(3) The monodisperse organic or inorganic spherical particles of a black color type achromatic color have a specific particle diameter, namely, a mean volume diameter (d) of 130 to 350 nm.
(4) When the surface of the particle laminate of the optical color-developing material constituted of, for example, organic polymer spherical particles is irradiated with visible rays, the vertically reflected light color visually sensed is a deep chromatic color, such as purple color, blue color, green color, yellow color or red color.
(5) In case of (meth)acrylic polymer monodisperse spherical particles, the vertically reflected light color visually sensed and the specific mean volume diameter (d) satisfy the following relationship:
(I) when d is in the range of 160 to 170 nm, the chromatic color developed is purple (P),
(II) when d is in the range of 180 to 195 nm, the chromatic color developed is blue (B),
(III) when d is in the range of 200 to 230 nm, the chromatic color developed is green (G),
(IV) when d is in the range of 240 to 260 nm, the chromatic color developed is yellow (Y), and
(V) when d is in the range of 270 to 290 nm, the chromatic color developed is red (R).
However, even if no crack is observed on the surface of the heretofore proposed particle laminate (or three-dimensionally ordered lattice) formed by drying a solid-liquid suspension and thereby arranging and aligning the dispersoid particles, there is a tendency that the ordered structure includes a layer wherein the particles are not sufficiently aligned longitudinally and laterally or that an ordered structure wherein the particles are aligned in different directions is formed, so that the ordered structure lacks structural homogeneity. In the existing circumstance, therefore, the properties exhibited have not been satisfied yet because of heterogeneity and a defective structure of the ordered structure.
Under such circumstances as mentioned above, the present inventors have earnestly studied in order to solve the above problems, and as a result, they have prepared an aqueous suspension using acrylic polymer colloidal particles which are monodisperse spherical particles of a black color type achromatic color having a mean volume diameter of 200 nm and containing carboxyl groups in a high concentration. The present inventors have found that a solid-liquid colloidal dispersion obtained by subjecting the above-prepared suspension having an electrical conductivity of 4000 μS/m to electrophoresis to reduce its electrical conductivity to 400 μS/cm and concentrating the resulting suspension to a volume concentration of colloidal particles of about 42% develops a chromatic color of clear red as a visually sensed color. Based on the finding, the present invention has been accomplished.
It is an object of the present invention to provide novel fluid colloidal crystals which comprise a solid-liquid dispersion, are used for producing a fluid ordered structure of organic or inorganic polymer spherical fine particles of colloidal particle size, and exhibit an excellent property reflection spectrum under irradiation with visible rays, ultraviolet rays and infrared rays.
It is another object of the present invention to provide a process for producing the above-mentioned novel fluid colloidal crystals.
It is a further object of the present invention to provide a process for producing a coating film of a three-dimensionally ordered lattice of spherical fine particles using a three-dimensionally ordered lattice which is extremely homogeneous as a particle array structure.